braced by cold, or
when relaxed by heat, must of necessity cause the timekeeper to go
either faster or slower, unless some method could be found to remedy
the inconvenience.

The method adopted by Harrison was his compensation balance, doubtless
the backbone of his invention. His "thermometer kirb," he himself
says, "is composed of two thin plates of brass and steel, riveted
together in several places, which, by the greater expansion of brass
than steel by heat and contraction by cold, becomes convex on the brass
side in hot weather and convex on the steel side in cold weather;
whence, one end being fixed, the other end obtains a motion
corresponding with the changes of heat and cold, and the two pins at
the end, between which the balance spring passes, and which it
alternately touches as the spring bends and unbends itself, will
shorten or lengthen the spring, as the change of heat or cold would
otherwise require to be done by hand in the manner used for regulating
a common watch." Although the method has since been improved upon by
Leroy, Arnold, and Earnshaw, it was the beginning of all that has since
been done in the perfection of marine chronometers. Indeed, it is
amazing to think of the number of clever, skilful, and industrious men
who have been engaged for many hundred years in the production of that
exquisite fabric--so useful to everybody, whether scientific or
otherwise, on land or sea the modern watch.

It is unnecessary here to mention in detail the particulars of
Harrison's invention. These were published by himself in his
'Principles of Mr. Harrison's Timekeeper.' It may, however, be
mentioned that he invented a method by which the chronometer might be
kept going without losing any portion of time. This was during the
process of winding up, which was done once in a day. While the
mainspring was being wound up, a secondary one preserved the motion of
the wheels and kept the machine going.

After seven years' labour, during which Harrison encountered and
overcame numerous difficulties, he at last completed his first marine
chronometer. He placed it in a sort of moveable frame, somewhat
resembling what the sailors call a 'compass jumble,' but much more
artificially and curiously made and arranged. In this state the
chronometer was tried from time to time in a large barge on the river
Humber, in rough as well as in smooth weather, and it was found to go
perfectly, without losing a moment of time.